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. Author manuscript; available in PMC: 2016 Dec 1.
Published in final edited form as: Ann Biomed Eng. 2015 Jun 16;43(12):2991–3003. doi: 10.1007/s10439-015-1356-x

FIGURE 4.

FIGURE 4

Ultrasound echoes from the internal and external boundaries of the three-layered hydrogel construct under 0 (blue) and 160 μm compression (red). The other three steps (40, 80, and 120 μm) are not shown in this figure. The maximum value of the normalized cross-correlation function was used to calculate the time delay between pre- and post-compression signals within a ROI. Three ROI windows (a 4–6 μs, b 8–10 μs, and c 12–14 μs) were selected to track the time shifts of the echoes reflected from the interfaces of the bottom to the middle gel, the middle to the top gel and the top gel to the acoustic reflector, respectively.